How would the US be effected by a Japanese nuclear meltdown?

If a nuclear reactor had a meltdown in Japan, what would happen to the United States? Would the radiation get here? I saw a map (not sure if it's legit or not), that said there'd be 750 RADS of radiation on the US west coast within 10 days. I don't know what that means, or if the map is even real, but should I be worried? Or would it even effect us at all? Thank you!